Combustion chamber with retrorse baffles for preheating the fuelair mixture



May l5, 1951 w. B. GlsT, JR 2,552,851

COMBUSTION CHAMBER WITH RETRORSE BAF'FLES FOR PREHEATING THE FUEL-AIR MIXTURE Filed oct. 25, 1949 w@ ,@W'J

ATTORNEY Paten-ted May 15, 1951 UNITED STATES PATENT OFFICE (LOMBUSTION` CHAMBER WITH RETRORSE BAFFLES FOR PREHEATING THE FUEL- AIR MIXTURE Application October 25, 1949, Serial No. 123,437

8 Claims. l

This invention relates to combustion apparatus, and more particularly to liquid fuel combustion apparatus for a gas power plant or the like.

In operation of combustion apparatus in a gas turbine engine, athodyd or the like, it is desirable to effect mixture of atomized fuel with air and rapid preheating of the mixture immediately before combustion thereof, for ensuring greater combustion efficiency and flame stability. Preheating of the fuel is usually a critical operation, due to the tendency to induce cracking of the fuel, and deposition of carbon on surfaces of the burner. It is an object of this invention to provide improved combustion apparatus constructed and arranged to effect rapid vaporizing and preheating of fuel and air `without cracking or deposition of carbon.

Another object of the invention is the provision of combustion apparatus adapted to promote the eilicient and stable combustion of fuel in a power plant under operating conditions that induce relatively low fuel pressures :and rates of air flow.

A further object is to provide combustion apparatus, in which stable combustion of fuel can be effected quickly enough to warrant reduction in length of the combustion chamber relative to that heretofore believed necessary.

Features of the -invention include the provision of an improved combustion assembly of relatively inexpensive lightweight construction, in which interposition of structural elements directly in the ame zone is avoided, and in which flow communications and orices are adapted to ensure uniform vaporization and combustion of fuel lwith minimum interference due to occasional presence of foreign particles in the fuel.

These and other objects are effected by the invention :as will be apparent from the following Fig. 3 is a, fragmentary sectional View taken `along the line AIII---III of Fig. 2, and indicating the section line II--II along -which the latter is taken.

The essential elements of -a typical aviation Vgas turbine power `plant are illustrated 'diagrammatically in Fig. 1, and comprise an outer casing structure I I, which may be made up of anumber of cylindrical sections :and which has suitably mounted therein an inner sectional core structure I2 cooperating with the outer structure to form an annular flow passageway I3, which extends longitudinally through the engine from a forwardly-directed intake opening I4 to a rearwardly-disposed discharge nozzle I5. It will be understood that the casing structure I I is adapted 'to be mounted in vor on the fuselage or wing of an aircraft, with the inlet opening I4 pointed forwardly. Operating elements of the gas turbine engine are arranged in axial alignment in order to minimize the frontal area presented by the engine, vand include an axial-flow compressor I'9, combustion apparatus 2D, illustrated in annular form, and a turbine 2l, which isV operatively connected to the rotor of the compressor through the medium of an axially disposed shaft 22.

In Vaccordance with well-known principles of operation of gas turbine power plants, air entering 'the annular intake opening III passes to the compressor I9, which delivers the air under pressure through the Ypassage I3 to the combustion Vapparatus 2IJ for supporting combustion of fuel, which `may be admitted by means hereinafter described. Heated motive fluid thus generated in the combustion apparatus 20 is then expanded through the turbine 2l for driving the compressor, `while the exhausted motive uid is discharged to the atmosphere by way of the nozzle I5, and may be in the form of a jet establishing a propulsive thrust.

According to the invention, the combustion apparatus may be of the unitary annularI type, or may if preferred include a plurality of separate combustor chambers or cans In the annular form chosen for illustration, the combustion apparatus 2U comprises an outer annular burner wall 25, which may be an assembly of overlapped graduated sections forming air inlet slots or apertures 26 communicating with an interior combustion chamber 2l, `and an inner annular burner `wall 28, consisting of similarly arranged sections providing air inlet slots 29, the wall assembly lbein-g supported from the casing structure Il by suitable struts, such as a hollow strut 30. Mounted within the frontal annular entryway 21a of the combustion chamber 2l are two radially spaced Vouter and inner annular substantially U-shaped -lchannel sections 33 and 34, which may be supported on the strut 30 with the concave surfaces thereof facing in an upstream direction while the opposite sides thereof are exposed within the vbe slightly richer than stoichiometric. mensions of the combustion chamber are preferably such as to promote relatively low air velocity,

2,552,851 j i i combustion chamber 21. Each of the channel sections 33 and 34 has a short annular side a, which may be secured to the adjacent end of the corresponding-burner wall or 23, and a relatively long side b, which may be generally frustoconical in form and extends forwardly, as shown. A pair of outer and inner frusto-conical flow divider baille structures 3S and 31 are also carried on the strut in spaced alignment with the respective channel sections 33 and 34, further enclosing the annular entryway 21a of the combustion chamber, and carrying an annular foraminous wall or baille 38 having apertures spacedV for slightly impeding ilow of air from the passageway I3 to the entryway 2id, for a purpose hereinafter explained. The respective'iio-w divider bafe structures 36 and 3l have mounted in the rearlnost portions thereof outer and inner fuel manifolds 40 and 4 lV which communicate through pipes 40a and 4Ia with a suitable fuel system (not shown). The manifolds 4Q and 4i are adapted to' supply fuel into curved annular preheating passages 42 and e3, respectively, by way of suitable .ejecting means, such as circumferentially spaced nozzles or orifices formed in the downstream sides of the manifolds.

In operation, as air delivered by the compressor i9 flows from the passageway I3 through the foraminous baille 38 into the entryway 21a of the combustion chamber, the impedance effect of the baffle 38 produces a local zone of relatively low air velocity and pressure on the downstream side thereof, increasing turbulence within the entryway, and causing air to be drawn inwardly from the passageway by way of the curved preheating passages 42 and 43, picking up and vaporizi-ng fuel issuing from the orifices 45. In practice, for example, eight or nine pounds of air flowing through the baffle 38 for each pound of fuel supplied by wayof the manifolds 40 and 4| may be expected to induce flow of about liveY pounds of air per pound of fuel through the preheating passages 42 and t3. As the air in the preheating passages pivots around the manifolds and reverses in direction of flow toward the Zone of local turbulence and low pressure, the fuel sprayed across the air stream onto the hot channelV sections 33Y and 3e is vaporized and swept along quickly enough to prevent cracking of the fuel and deposition of tars or carbon.

preheating passages 5.2 and 43 into the turbulentV zone or entryway 21a. and into the combustion chamber 2l, where combustion is further supported by air entering by way of the apertures 26 and 29. The air-fuel ratio in this zone should The diand consequently, a stable flame zone. Heat from the combustionrzone serves'to maintain the chan- .nel members 33 and 3e sufficiently hot to continue -vaporization of incoming fuel.

f It will further be seen that the improved combustion apparatus, constructed and operated as nhereinbefore described, will ensure uniform va- V'of fuels, including relatively inexpensive, commercially available fuels having high boiling points, such as kerosene. Y

vWhile the invention has been shown in but time form, it `will be obvious to, those skilled AVin .the

Y said combustion chamber and having fuel discharge orifices, wall means establishing separate flow paths in said passage on opposite sides of said manifold, an annular retrorse baille mounted between said combustion chamber and said manifold and forming a preheating passage having an air entryway communicating with one of said Vflow paths and an air outlet communicating with said other flow path, and flow impeding baille means interposed in the last-mentioned flow path for effecting reduction in air pressure at said air outlet for establishing a current of air Vthrough said preheating passage to pick up and vaporize fuel from said manifold in initial heat exchange relation with said baille, prior to flow lof the heated air and fuel mixture into said comdownstream of said manifolds, respectively, each of said manifolds having means for effecting the spraying of Vfuel onto the respective bailles for abstracting heat therefrom, and a foraminous baffle interposed in said central ilow path for effecting local turbulence and reduction in pressure of air inducing continuous flow of air from said outer llow paths to sweep the sprayed and heated fuel into said combustion chamber.

Y 3. Combustion apparatus comprising substantially cylindrical wall and core structure forming an annular air supplyV passage, innerV and outerv apertured combustor walls mounted in spaced coaxial relation in said passage for providing an annular combustion chamber having an upstream entryway, concentric inner and outer annularV channel members mounted adjacent the respective combustor walls and having concave surfaces facing upstream and terminating within said entryway, said channel members being subject to heat from said combustion chamber, fuel supply means aligned with the concave surfaces of said channel members and spaced upstream thereof, and means interposed in the path of air flowing from said supply passage into said entryway for effecting reduction in air pressure in 'said entryway, thereby inducing flow of air from said passage past'said fuel supply means and said channel members for rapidly mixing fueland air with initial transfer thereto of. heat from said channel members prior to ilow thereof into said combustion chamber.

4. Combustion apparatus comprising substantially cylindrical wall and core structure forming an annular air supplyrpassage, innerV andouter apertured combustor walls mounted in spaced coaxial relation in said passage for providing an annular combustion chamber having an upstream entryway, concentric inner anndnouter annular channel members having substantially U- shaped cross sections and mounted adjacent said combustor walls, respectively, in heat transfer relation with respect to said combustion charnber, spaced concentric annular flow dividing baffle structures supported in said air supply passage and terminating in fuel manifolds having discharge orifices disposed upstream of the respective channel members, said baille structures and corresponding channel members forming curved annular preheating passages communieating with said air supply passages and discharging into said entryway, and an annnular apertured baile extending across the space between said baille structures upstream of said entryway, whereby flow of air from said supply passage to said entryway is throttled to effect reduction in pressure in the latter for drawing air thereto from said supply passage through said preheating passages along with vaporized fuel from said manifolds.

5. Combustion apparatus comprising boundary wall structure providing an air supply passage, interior wall structure disposed therein and forming a combustion chamber, a fuel manifold mounted upstream of said combustion chamber and having fuel discharge orifices, and a curved re-entrant baille interposed between said cornbustion chamber and said fuel manifold, said baille and manifold forming a preheating passage having an air entryway communicating with said air supply passage and an outlet communieating with said combustion chamber, whereby a path for air is established through said preheating passage for effecting vaporization of fuel discharged from said manifold in initial heat exchange relation with said baliie prior to flow of the heated air and fuel mixture into said cornbustion chamber.

6. In combustion apparatus including an annular combustion chamber and an annular air supply passage communicating therewith; spaced concentric inner and outer annular fuel manifolds mounted upstream of said combustion chamber and having fuel discharge orifices, wall means establishing separate outer flow paths in said passage outwardly of said manifolds and a central flow path therebetween, and concentric annular re-entrant baiies subject to heat of combustion in said combustion chamber and spaced downstream of said manifolds, respectively, each of said manifolds having means for effecting the spraying of fuel on the respective baffles for abstracting heat therefrom, whereby air flowing from said outer low paths is mixed with fuel preheated during contact with said baffles prior to delivery to said combustion chamber along with air from said central flow path.

7. Combustion apparatus comprising boundary wall structure providing an air supply passage, interior wall structure disposed therein and forming a combustion chamber, a fuel manifold mounted upstream of said combustion chamber and having a fuel discharge orifice, a curved reentrant baffle interposed between said combustion chamber and said fuel manifold to provide a preheating passage from said air supply to said combustion chamber, and an auxiliary duct structure having `flow-limiting passages disposed within said boundary wall structure and extending upstream with respect to said baille for effecting supply of air at reduced pressure from said air supply passage to said combustion chamber adjacent the outlet end of said preheating passage, whereby air is caused to flow through said preheating passage to sweep vaporized fuel into said combustion chamber,

8. Combustion apparatus comprising substantially cylindrical wall and core structure forming an annular air supply passage, inner and outer apertured combustor walls mounted in spaced coaxial relation in said passage for providing an annular combustion chamber having an upstream entryway, concentric inner and outer annular channel members having substantially U-shaped cross sections and mounted adjacent said combustor walls, respectively, in heat transfer relation with respect to said combustion chamber, and spaced concentric annular flow-dividing baffle structures supported in said air supply passage and terminating in fuel manifolds: having discharge orifices disposed upstream of the respective channel members, said baffle structures and corresponding channel members forming curved annular preheating passages communieating with said air supply passages and discharging into said entryway, whereby flow of air from said supply passage to said entryway is throttled to effect reduction in pressure in the latter for drawing air thereto from said supply passage through said preheating passages along with vaporized fuel from said manifolds.

WILLIAM B, GIST, JR.

No references cited. 

